I made sure I had him look it up on the computer before I spent a ton of money on Royal Purple fluids. He told me its plain old 75/90 gear oil. 4 quarts of that is around $60. I put it in and been driving it a couple days. It seems nice and smooth and shifts great. I want to get the right stuff in the getrag which I know now is 10/30, but is it pretty safe for me to run the 75/90 for the next 2 days till I get a chance to change it out again?

 

I'd get it out of there. The thicker 75-90w cannot oil (very well) into the pocket bearing between the input and mainshaft. Granted we're not really cold outside at the moment, but that could change tonight. You may also have the clutch/ friction material style syncros that wont understand the difference in lubricity. Get 5w-30 or 10w-30 RP and dont forget to add an extra quart thru the shift tower hole after you put in the plug.

 

For the Getrag the correct oil as I understand is 5-30 motor oil, use a full synthetic, Mobil 1 is best for towing and Royal Purple SYNCHROMAX is what to use for a "fun truck", For overfill its between 4.5 and 5 quarts, I am running 5 quarts of Mobil 1 5-30 in mine, feels great. Hope I helped ya!

D-C out!


PS the heavy stuff will starve the bearings, especialy when cold, Get it out!!!!!!!!!

 

Then again there are many owners that have run 80-90wt for hundreds of thousands of miles with no problems. You should be fine til you get a chance to drain it. I use 15w40 with no issues only because I have more of it around.

 

before I found this site (yes Im gilty) I ran 85 90 (something like that) oil in my getrag for 100,000 miles plus. No problems

and yes I do use my truck 10ft camper 17ft jetsled

 

i ran 80 90 shell hauling a car hauler and loaded truck across country. Virginia to San Diego. no problems here.

 

Well if I can get away with it I may just leave it. With a quarter million miles I'm sure there is some slack in there and the thick oil can fill it. lol RP fluids are thinner than other oils too so I guess it may be fine. I drive 70 miles each way to work and after I got home I felt the trans and it felt prety warm. Not too hot I couldnt hold my hand on it, but it was warm. Is that normal?

 

I have that with my NV4500, its the nature of the beast, when you get that many parts rubbing together under any decent load things are going to heat up...over a 70mi trip if its not too hot to touch your fine.

 

You're probably fine for now but remember to take it easy on it when it's cold or you might starve a bearing for lube. Hot shouldn't be a problem.

I use 5 qts of Castrol Syntec 5W50 in mine and when towing, it'll get close to 200* case temp according to my IR thermometer. You sure want good oil in there at those temps.

 

My truck was dealer mantained and when I went to change the fluids after getting it it was 90w. Worked fine............it puked but it had nothing to do with liquids.